ABSTRACT: The fundamental purpose of this study was to investigate the usefulness of anti-hepatitis B vaccination campaigns in the prison population, considering: 1) the vaccine's immunogenicity and 2) the feasibility of the programme itself (acceptance of pre-vaccination serologic screening and compliance of the vaccination schedule). Prior to vaccination, the prevalence of hepatitis B virus (BBV) markers was studied in 1,742 male prisoners in 3 different types of prison centre (PC) in Catalonia. This number of prisoners represents over 98% of these PCs total population. Marker presence was related to a series of variables (demographic, prison and infection risk factors), obtained by means of personal guided interviews. In 63% of prisoners, some kind of HBV marker was detected, which was HBsAg in 7.1%. Parenteral drug consumption (POC) was the factor most strongly associated with BBV infection (raw OR 7.35, IC95% 5.84+9.27) .The different serologic patterns of the seropositive subjects (except the prevalence of anti-HBs alone), were more common in those practising PDC. It was possible to give two thirds of the prisoners 2 vaccine doses, and one-third 3 doses, obtaining seroconversion rates and anti-HBs titres moderately lower than those obtained in groups of healthy population. Advanced age, PDC and BIV infection cause a worse response. The prior presence of anti-HBs alone does not have any influence. Vaccination of prisoners against hepatitis B allows the conventional health networks to act on population groups that otherwise would be difficult to reach, thus protecting these people both inside and outside the prison. In order to improve vaccination schedule compliance, the use of flexible systems is suggested, 0, 1 and 2 months being the reference system.